This invention relates generally to a safety apparatus for protecting a vehicle passenger in a collision of the vehicle by inflating a bag against the passenger, and more particularly to an improved inflatable bag for such apparatus.
It is expected that apparatus comprising an inflatable bag as a main element thereof will occupy an important position in the field of safety measures for protecting passengers in various vehicles subject to impact, particularly in automobiles, in the near future. In a collision of the vehicle, the bag is rapidly inflated by a pressurized gas towards a passenger or seat occupant to provide cushion against an inertial movement of the occupant. Merits of such apparatus have been ascertained, but a problem remains unsolved. When the passenger bumps against the inflated bag, the bag repels the passenger with a considerable magnitude of force resulting from a sharp increase in the internal pressure of the bag.
Various means have been proposed until now to prevent a gas pressure in the bag from increasing excessively and protect the passenger from possible injuries due to repelling by the bag, but none of the prior art is considered fully satisfactory. A bag, for example, equipped with a relief valve which operates at a predetermined pressure has been proposed. In practice, however, a considerable dispersion is observed in the relieving pressure of the valve attached to the inflatable bag apart from a natural increase in the production cost. Also it has been proposed in regard to a bag of a wooven fabric to provide a specific region on the bag where the texture of the fabric is loosened in such a calculated manner as to give vent to the confined gas when the gas pressure in the bag exceeds a predetermined pressure. Although the provision of no extra valve means is necessary, this bag itself is not easy to produce and it is quite difficult to design an appropriate texture for realizing such a region and calculate an optimum area of the region. According to a still another method, it has been intended to cut open a bag locally with an edged tool which is arranged outside the bag such that the tool pierces the bag when the bag is bumped by a passenger and swerved. This method also has the disadvantage of an extremely complicated construction. In a slightly different but similarly purposed method, a plurality of needle holes are formed on a portion of a bag in a circular alignment. The bag material rips along the hole line and gives an opening at a critical bag pressure, but the critical pressure exhibits a considerably large dispersion in practical applications.